Increased use of Internet based applications and e-commerce transactions result in increased volume of data being exchanged between users. Accordingly, the demands for large network storage space are on the rise as well as a need to provide means for effectively sharing large quantity of information at a higher data transmission speed. This is addressed by employing technologies such as network-attached storage (NAS) and storage area network (SAN) systems.
However, a significant difficulty in providing storage is not in providing the large quantity of storage, but in ensuring that storage capacity is provided in a manner that enables ready and reliable access to data with simple interfaces. Large capacity, high availability and high reliability storage systems typically involve complex topologies of physical storage devices and controllers. Large capacity storage systems are those having greater capacity than single mass storage devices. High reliability and high availability storage systems refer to systems that spread data across multiple physical storage systems to ameliorate risk of data loss in the event of one or more physical storage failures. Both large capacity and high availability/high reliability systems are made possible by high end storage devices such as redundant array of independent disk (RAID) systems.
Associated with the use of high end storage devices, is a virtualized storage system which provides transparent abstraction of storage at the block level. It is possible to generate and maintain backup copies of data on the storage devices in the virtualized storage system in a manner that ensures that the enterprise demands for data (e.g., security, large capacity and high availability) are met. Techniques like snapshot operations are implemented on the virtualized storage system to ensure that the above demands are met. A snapshot operation creates a new logical disk called snapshot logical disk (also referred in short, as snapshot). A snapshot is a point-in-time readable/writable consistent copy of the data in the original logical disk which is created substantially instantaneously.
When a snapshot is created, no user data needs to be copied. Instead, a sharing relationship is created between the snapshot and the original logical disk. A first update to any data in either the original logical disk or the snapshot results in a prior copying of the corresponding data from the original logical disk to the snapshot. This is sometimes referred as Copy on First Write (COFW) operation.
A variation of the snapshot operation is called snapclone operation wherein a permanent copy of the logical disk is created for normal and interactive use. This is termed as the snapclone logical disk or in short, snapclone. The snapclone operation employs similar techniques and mechanisms used in the snapshot operation with one additional feature, wherein, the snapclone copy processes are typically run in the background on the virtualized storage system with appropriate priority to ensure that almost no disruption happens to user I/O requests. These snapclone copy processes copy the data from an original logical disk to a snapclone logical disk in its entirety.
A disadvantage of the current snapclone operation (similarly applicable to the current snapshot operation) is its inability to distinguish two different contexts in which a clear bit operation is performed on a sharing bitmap associated with the snapclone operation. For example, in a scenario where no user I/O requests are issued while a snapclone operation is in progress and the original virtual disk is one terabyte in size, a complete snapclone operation involves copying over one million (1024*1024) segments (i.e. one segment is equivalent to one megabyte) of data to the snapclone virtual disk and performing one million synchronous writes (updates) to the on-disk sharing bitmap. This can lead to significantly large number of I/O operations thereby degrading the overall performance of the virtualized storage system.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.